libxcrypt: Fix windows cross

`pkgsCross.mingwW64.libxcrypt`

`isWindows` because
> MinGW does not allow building shared libraries (DLLs) when there are still unresolved symbols, because on Windows each symbol referenced from a DLL must point to something that exists. On other platforms this is not always required.

https://stackoverflow.com/questions/69214347/libtool-error-cant-build-x86-64-w64-mingw32-shared-library-unless-no-undefin

So i presume this is needed for all windows toolchains.

pkgs/development/libraries/libxcrypt/default.nix

@@ -28,6 +28,9 @@ stdenv.mkDerivation (finalAttrs: {
     "--disable-werror"
   ];
 
+  # fixes: can't build x86_64-w64-mingw32 shared library unless -no-undefined is specified
+  makeFlags = lib.optionals stdenv.hostPlatform.isWindows [ "LDFLAGS=-no-undefined"] ;
+
   nativeBuildInputs = [
     perl
   ];